20 Nov
2007
20 Nov
'07
10:57 p.m.
Hi,
I'm attempting to use dlsym to dynamically load a ladspa plugin lib in
c++. I've found various web pages describing how to use dlsym in c++
but they do not seem entirely relevant to using ladspa (ie ladspa
plugins are mainly written in c) (??).
I've also looked at some ardour src, but somehow it seems to use, in a
c++ file, the c method which should not work (!?). I also looked within
hydrogen src, but that seems to use QT(?) to do the loading - and
delving into the QT src code does not appeal right now ;-)
Anybody know where could I find some simple c++ source examples for
loading ladspa plugins?
Cheers,
James
21 Nov
21 Nov
6:48 a.m.
On Tuesday 20 November 2007 21:57, james jwm-art net wrote:
I'm attempting to use dlsym to dynamically load a
ladspa plugin lib in
c++. I've found various web pages describing how to use dlsym in c++
but they do not seem entirely relevant to using ladspa (ie ladspa
plugins are mainly written in c) (??).
Are you wrapping your C++ code in the '#extern "C" {}' keyword? This is
necessary in order to keep the C++ compiler from mangling the names. A good
overview of how it all works (specific to Solaris, but good info for Linux as
well) can be found at:
http://developers.sun.com/solaris/articles/external_linkage.html
Cheers!
|-------------------------------------------------------------------------|
| Frederick F. Gleason, Jr. | Chief Developer |
| | Paravel Systems |
|-------------------------------------------------------------------------|
| To invent, you need a good imagination and a pile of junk. |
| -- Thomas Edison |
|-------------------------------------------------------------------------|
7 a.m.
On Wed, 2007-11-21 at 02:57 +0000, james jwm-art net wrote:
Hi,
I'm attempting to use dlsym to dynamically load a ladspa plugin lib in
c++. I've found various web pages describing how to use dlsym in c++
but they do not seem entirely relevant to using ladspa (ie ladspa
plugins are mainly written in c) (??).
The LADSPA interface is defined in terms of C structures and types, so
the language used to write the plugin doesn't matter to the loader.
dlsym() is what you use. Strictly speaking it should not work in a
standards-compliant compiler without some ugly tricks since casting void
pointers (which is what dlsym() returns) to function pointers is not
allowed in C++, but fortunatly most compilers are not that strict about
it.
If you really want your code to work in a strict compiler you can do
something like
union {
void* in;
LADSPA_Descriptor_Function out;
} foo;
foo.in = dlsym(lib_handle, "ladspa_descriptor");
LADSPA_Descriptor* descriptor = (*foo.out)(0);
...
which will not generate any errors, but _will_ invoke undefined
behaviour. It works on all platforms I've tried though.
--ll
12:17 p.m.
Thankyou, that does the trick.
You can expect to see a new release of "Wav Composer Not Toilet"
soonish.
It will include selected LADSPA plugins - hardcoded - so plugins not
supported will not be available.
and mandatory dependancy on libsndfile for all wav reading/writing.
Which should hopefully make it a whole lot nicer.
Dunno why I've been so scared of doing this, it's not so complex after
all :)
Cheers,
James.
On 21/11/2007, "Lars Luthman" wrote:
On Wed, 2007-11-21 at 02:57 +0000, james jwm-art net
wrote:
Hi,
I'm attempting to use dlsym to dynamically load a ladspa plugin lib in
c++. I've found various web pages describing how to use dlsym in c++
but they do not seem entirely relevant to using ladspa (ie ladspa
plugins are mainly written in c) (??).
The LADSPA interface is defined in terms of C structures and types, so
the language used to write the plugin doesn't matter to the loader.
dlsym() is what you use. Strictly speaking it should not work in a
standards-compliant compiler without some ugly tricks since casting void
pointers (which is what dlsym() returns) to function pointers is not
allowed in C++, but fortunatly most compilers are not that strict about
it.
If you really want your code to work in a strict compiler you can do
something like
union {
void* in;
LADSPA_Descriptor_Function out;
} foo;
foo.in = dlsym(lib_handle, "ladspa_descriptor");
LADSPA_Descriptor* descriptor = (*foo.out)(0);
....
which will not generate any errors, but _will_ invoke undefined
behaviour. It works on all platforms I've tried though.
--ll
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3 comments
3 participants
participants (3)
-
Fred Gleason -
james jwm-art net -
Lars Luthman